1. Field of the Invention
The present invention pertains to the field of heat dissipation in an electronic device. More particularly, the present invention pertains to the use of multiple heat dissipation mechanisms to cool one or more electronic components.
2. Description of Related Art
Faster and more powerful computer components allow the design and construction of higher performance portable computing devices such as laptop or notebook computers. Unfortunately, the use of such faster and more powerful computer components often results in increased heat generation by such computing devices.
Additionally, as some computer components shrink and/or increasing computer component integration shrinks overall computer size, electronic components may be arranged in a more compact form. Such increasing component density coupled with decreasing overall computing device size inherently decreases space available for convective airflow and accordingly raises heat dissipation concerns. Thus, improved heat dissipation technology is often needed to maintain operating temperatures within an acceptable range in smaller and/or more powerful portable computing devices.
Maintaining operating temperatures of computer system components below certain levels is important to ensure performance, reliability, and safety. Most integrated circuits have specified maximum operating temperatures, above which the manufacturer does not recommend operation. Additionally, transistors on an integrated circuit tend to slow down as operating temperature increases. Thus, a computer system that operates its integrated circuits close to or beyond recommended timings may fail as temperature increases.
Additionally, integrated circuits may be physically damaged if temperatures elevate beyond those recommended. Such physical damage obviously can impact system reliability. Finally, the computer system casing should be kept at a temperature which is safe for human contact. This may necessitate spreading of heat throughout a computer system base or efficiently expelling heat to avoid hot spots near certain components such as a processor.
One prior art technique for cooling an electronic component in a portable computing device is to conduct heat from the electronic component to a plate beneath the device""s keyboard using a heat pipe affixed by a heat conductive block to the electronic component. As increasing amounts of heat are generated by the electronic component, this technique may cause the plate beneath the keyboard and hence the keyboard to reach temperatures which are too hot for safe or comfortable use. Thus, such passive heat dissipation techniques may prove insufficient in some applications.
Active techniques have also been employed to cool electronic components in portable computing devices. One example of a prior art active heat dissipation technique is to use a fan based heat exchanger. In one prior art approach, a thermal connection exists between an electronic component and a fan based heat exchanger having heat dissipation fins. The thermal connection includes a thermal block connecting the electronic component to the heat pipe and, in some cases, the heat pipe being connected to the heat dissipation fins through an outer casing of the heat exchanger.
Each additional element in the thermal path from the heat generating component to the heat dissipation mechanism may result in decreased thermal conductivity between the electronic component and the heat dissipation fins. As a result, a thermal path from the electronic component to the fins having numerous elements may be somewhat inefficient. Moreover, if active heat dissipation is the only mechanism provided for heat dissipation, the active dissipation is likely necessary when the portable computing device is relying on battery power. Consequently, the active thermal solution may disadvantageously drain the battery.
Thus, the prior art does not adequately combine multiple heat dissipation mechanisms to cool portable computing devices. The prior art also does not provide a combination active and passive thermal solution which enables the active dissipation mechanism at a varying power level based on temperature and/or power source. Furthermore, the prior art does not demonstrate the use of multiple heat dissipation mechanisms where a passive heat dissipation mechanism is coupled to a heat generating component by a thermal path having a limited thermal conductivity portion to limit the amount of heat dissipated by the passive heat dissipation mechanism.
A heat exchanger is disclosed. The heat exchanger includes a first heat dissipation mechanism having a first heat dissipation capacity and a second heat dissipation having a second heat dissipation capacity. At least one heat transfer mechanism thermally couples the first heat dissipation mechanism and the second heat dissipation mechanism to a heat generating component. The heat transfer mechanism has a limited conductivity portion in the thermal path to either the first or the second heat dissipation mechanism.